We report a new method for protecting nucleosides for hydrogen phospho
nate RNA synthesis that gives very high yields for the purines. This m
ethod is based on our finding that, for adenosine and guanosine, silyl
ation of a mixture of 2' and 3' H-phosphonates in the presence of DBU
is highly selective for the 2' hydroxyl. (C) 1997 Elsevier Science Ltd
.